1. Field of the Invention
This invention relates generally to pistons and syringes, and, more particularly to industrial pistons and syringes and even more particularly to such pistons and syringes made of pliable materials, for example plastics.
2. Background Information
Plastic syringes have been finding increasing use in industrial applications requiring precise dispensing of a wide variety of fluids. Plastic syringes are finding favor since they are disposable and relatively inert to many solvents and other material being dispensed. Moreover, the pliable plastic pistons allow the release of air trapped in the syringe barrel, prior to dispensing, around the piston itself prior to and during the dispensing of fluids. The air free syringe combined the technology of the dispensing apparatus provide accurate and repeatable dispensing volumes. The materials being dispensed may have a wide range of viscosities from very viscous, like epoxies, to water.
Typically the syringe is filled with a viscous fluid that traps air near the piston. With viscous fluids the approach of tipping the syringe needle point outlet up to allow the air to rise is not efficient because it takes too long. The more typical approach is to manually drive the piston as if to dispense the fluid but to do so that the pressure and the pliable piston and syringe body allow the trapped air to escape around the piston.
However, it is the pliable plastic materials that provide the advantage of allowing air to bypass the piston present some limitations that are proving troublesome in practice. One such problem occurs when larger diameter pistons are used and/or high pressures occur in the barrel of the syringe. In such cases the fluid tends to bypass or xe2x80x9cblow byxe2x80x9d the piston. xe2x80x9cBlow byxe2x80x9d refers to the material meant to be dispensed traveling around the piston (as the air did as described above) thereby infiltrating and eventually destroying repeatability and accuracy of the dispensed volume. When dispensing fluid by driving the fluid out the needle output, the pressure acts in all directions including trying to drive the fluid around the piston where the piston and the syringe body intersect. High enough pressure will overcome the pliable material resistance and will force the fluid around the piston causing the blow by problem. The blow by problem occurs in virtually in all syringes, but it occurs more often and is more of a problem in higher volume dispensing systems using large diameter syringes. In particular industrial syringes in the 30 cc range and higher are especially susceptible to such problems and limitations because the piston diameters become large and the pressures and forces at the outer ends of the pistons where the piston meets the inner surface of the syringe body become large enough to distort the piston and or the syringe body. The large diameter syringe piston has a longer xe2x80x9cmoment armxe2x80x9d (the radius). It becomes easier to distort the piston by at the far edge due to the mechanical advantage of the longer moment arm. The pressure loss in the syringe combined with fluid exiting past the piston as opposed to out the needle point outlet destroys the systems accuracy and repeatability. Furthermore, it may damage the fluid dispensing equipment. Such fouling requires that the equipment be disassembled and cleaned or discarded.
Another limitation of known syringe dispensing systems occurs when the piston becomes cocked in the barrel of the syringe. When this happens the syringe may continue to function, but the dispensing amounts will be inaccurate and non-repeatable.
Another limitation of known syringe dispensing systems occurs when the piston is held stationary by a mechanical arm during dispensing creating pressure in the syringe chamber. Said pressure causes the outside edges of the plastic piston to deflect. This deflection will destroy accuracy and repeatability of dispensing outputs.
It is an object of the present invention to prevent cocking of the piston and xe2x80x9cblow byxe2x80x9d by providing a strengthening and stabilizing support that substantially prevents xe2x80x9cdeflection of the pistonxe2x80x9d in industrial syringes.
The object set forth above as well as further and other objects and advantages of the present invention are achieved by the embodiments of the invention-described hereinbelow.
The barrel stabilizer is an insert that mates with the piston in an industrial syringe. The piston is attached to the mechanized drive via a threaded engagement housed by the stabilizer. The stabilizer extends across the diameter of the piston thereby strengthening the piston to sustain higher pressures and dispensing quantities and increases the overall height to eliminate any possibility of the piston cocking inside the syringe.
The stabilizer is arranged to mount into the piston on the side not facing the fluid, in a preferred embodiment, after any trapped air has been eliminated. In a preferred embodiment the stabilizer is arranged as a split barrel that is assembled like a claim shell embracing the drive rod and supporting the piston. The two halves of the barrel may be joined by screws, belts or springs wrapped around the barrel, adhesives or other known techniques.
The stabilizer can be made from metal, wood, plastic or virtually any solid material that provides mechanical integrity for the pressures and forces involved. In a preferred embodiment, plastic is used.
For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims